The Ascending Reticular Activating System: The common root of consciousness and attention

In the organization of the central nervous system the role of Ascending Reticular Activating System (ARAS) – comprising the reticular formation, thalamus and thalamo-cortical system of bi-directional projection which governs the activities of wakefulness and vigilance – does not correspond to a hierarchical superiority with respect to the cerebral hemispheres. The ARAS is not limited to the brain stem: it projects upwards towards the cerebral hemispheres and downwards towards the spinal cord. Its functions are much more complex than simple cortical desynchronization, even though this is essential in the state of alertness and attention. Its thalamo-cortical projections, which are a-specific with a high oscillatory frequency, are fundamental for some essential functions of consciousness.